1. Field of the Invention
The present invention relates generally to a process for molding or forming items from pulp, slurries, or other suspensions and products obtained thereby. The vacuum mold head or mold plate in the apparatus is given the ability to be located in various orientations within the material holding tank, thereby creating the ability to control the vortex created during the molding process. By controlling the vortex the material properties can be controlled, particularly, when utilizing slurries with low solids concentrations.
2. Related Art
The forming process of items, particularly those formed from solutions of pulps, slurries or suspensions have, up to now, never had a way to control the direction of gravity during the forming process. In the prior art, once the mold was set up, the direction of gravity was fixed relative to the mold. Gravity effects on the suspended particles in the suspensions would, during the forming process, sometimes cause non-Page uniform surface effects in the formed piece. What is needed in the art is a mechanism to control the orientation of the vacuum mold head relative to gravity.
The use of a vacuum mold head is well known in the art. In co-pending U.S. patent application Ser. No. 11/106,096 a device with an articulating, or gambrel, arm is described along with the ability to control the orientation of the vacuum mold head relative to gravity. This advance in the mechanism has led to further understanding in the dynamics of fiber deposition and allowed further advances in the properties which can be obtained.
Through diligent research it has now been realized that fibers can be selectively oriented by controlling the motion of the vacuum mold head to increase the physical strength of the final product.
Vacuum forming techniques are characterized by the use of a mold head which has a vacuum, or suction, applied to one side of the mold head. The mold head is lowered into a slurry of fibers. As the slurry is drawn through the mold head the fibers deposit thereby forming the preform by depletion of the solids in the slurry. The solvent, typically with some concentration of fibers, passes through the filter and is either discarded or recycled. It is widely known that the slurry tends to form a vortex due to the act of drawing the slurry through a void. In extreme cases when the fiber, or solids content is very low, the vortex is approximately centrally located over the vacuum port. In many cases the impact of the vortex can be measured as variations in thickness from the center of the vortex outward. There have been many attempts to alleviate this problem by techniques such as varying the sizes of the voids, using baffles in the slurry, introducing air flow into the slurry to disrupt the local flow and other techniques. These techniques are insufficient and difficult to set up. Baffles, for example, are widely used. The location of the baffles is typically done by trial and error which requires a substantial amount of effort. If the product is changed the baffling must also be changed in ways which are not easily predicted. This leads to wasted time and effort and makes it difficult to quickly change from one product to another. Furthermore, the baffles are typically fixed relative to the tank, and within the solution, which limits changes during the fiber deposition process.
Even with the best efforts current techniques are not sufficient and tend to be counterproductive by slowing the formation process. Depending on the shape and design of the mold head the vortex formation can be localized with a vortex for each void or it can be larger with a vortex covering larger areas of the filter. The vortex causes fibers to congregate and at least partially align approximately tangentially to the vortex within the slurry. This tangential alignment of fiber or solids may be used to increase the preform thickness in desired areas without baffling which tends to slow the formation process. As the fibers reach the filter there is, at least, localized fiber orientation or alignment. As would be realized fibers which are parallel and overlaid do not form a strong matrix and must be cross-linked, or cured, to represent a rigid structure.
Through diligent research the present inventor has developed a process for slurry molding applications which can disrupt localized fiber alignment with minimal efforts and without reliance on baffles or flow control techniques. Furthermore, the disruption provides a product hypothesized to have fibers oriented in a manner which approaches randomness and which are interlaced resulting in significant increases in strength relative to conventionally formed slurry molded products.